This invention relates to a production method of a semiconductor device, and more particularly to a production method of a connecting layer of the semiconductor device.
According to the recent remarkable progress in seeking higher integration and higher operation speed, the integration pattern of a semiconductor device has become excessively minute and of a high density, so that the effective area required for connecting electrodes thereof is also tending to be increased inevitably. At present, aluminum and aluminum alloys which are economical and have low electrical resistance are widely used for connecting purposes. However, in a case where aluminum or an aluminum alloy is used in a VLSI as a connecting material, the following problems usually occur.
As a pattern becomes minute, the width of each connecting line is reduced. However, the voltage applied to the integrated circuit is held to, for instance, DC 5V, and hence electrical stress caused in the conecting line tends to increase. As a consequence, connecting line troubles frequently occur due to electromigration and the like when the line is made of aluminum or aluminum alloy.
As the second problem, the melting point of aluminum or aluminum alloy is comparatively low, being approximately 450.degree. C., and therefore the temperature in the subsequent production steps must not exceed the melting point, thus reducing the productivity of the integrated circuit.
As the degree of integration increases, a multilayer arrangement of connecting conductors becomes essential. Since aluminum or aluminum alloy cannot ordinarily resist the temperature required for the formation of the interlayer insulating film, there is a restriction in selecting a suitable insulating film to be used between the connecting conductors, and the reliability of the multilayer connection is thereby impaired.
In order to obviate the above described difficulties of aluminum or aluminum alloy, a silicide film of a refractory metal has also been tried recently. Such a film can be easily obtained by firstly forming a layer of a refractory metal on a polysilicon film by a sputtering method or the like, and then annealing the layer in a temperature range of from 450.degree. C. to 600.degree. C. Alternatively, the silicide film of a refractory metal may be made directly by a CVD method using, for instance, tungsten hexafluoride (WF.sub.6) and silane (SiH.sub.4). However, the silicide film of a refractory metal has a line resistance as high as 10 to 100 micro-ohm/cm, which is much higher than the line resistance of aluminum which is approximately equal to 2.3 micro-ohm/cm.
In order to overcome this difficulty, a refractory metal film other than the above described silicide type, which is stable at a high temperature and exhibits a lower line-resistance than that of the silicide film is now studied intensively.
For the production of such a refractory metal film a sputtering method, a chemical gas-phase growing method (CVD methods) and the like are considered. The sputtering method is advantageous because a refractory metal film of an excellent quality can be produced. However, the target made of pure refractory metal is extremely expensive, and hence the method cannot be exercised practically. On the other hand, the CVD method permits to production of the refractory metal film at a comparatively low cost. However, the refractory metal film formed by the CVD method of an insulating layer made of, for instance, silicon dioxide (SiO.sub.2) has exhibited an insufficiency in bonding with the underlying layer, thus making it difficult to use this method practically. Although there has been proposed a method wherein a connection pattern is firstly formed on an insulating layer by use of a polysilicon film, and the refractory metal film is thereafter formed on the connection pattern in accordance with the CVD method, such a method has complicated the production steps.